Rubbers are typically compounded with numerous chemical agents prior to being molded and cured into desired articles of manufacture. The rubber compounding procedure utilized is normally carried out in a mixing device which relies on shearing forces, such as a Banbury mixer or a mill mixer. During this compounding procedure, the rubber is commonly mixed with sulfur, accelerators, carbon black, antidegradants, and other desired rubber chemicals. It is also very common to blend more than one type of rubber in the compounding procedure.
The high shearing forces required to attain homogeneous mixtures result in a degradation of the rubber. For this reason, the Mooney viscosity of the rubber being compounded decreases during the mixing procedure. This problem becomes more serious in rubber compounds which contain reinforcing materials, such as carbon black, which are included to increase the modulus of the rubber. For instance, rubber compounds which contain large amounts of carbon black are particularly difficult to process. Nevertheless, it is often necessary to include significant amounts of carbon black in rubber compounds to attain the desired modulus.
Processing oils naturally improve the processability of rubbers. However, the inclusion of processing oils in such rubbers results in a decrease in modulus. Accordingly, the inclusion of substantial amounts of processing oils in rubber compounds is frequently not a viable option for attaining good processability. High rubber performance requirements have traditionally necessitated compounding rubbers which have very poor processability characteristics.